Hermetic rotary compressors include, as main components, a hermetic container, an electric motor provided in the hermetic container, and a compression unit arranged in the hermetic container and driven by the electric motor to compress refrigerant gas. The electric motor includes a rotor firmly fixed on a crankshaft extending from a rocking scroll in the compression unit and a stator fixed to the hermetic container. Such a hermetic rotary compressor sucks the refrigerant gas into the compression unit and compresses the refrigerant gas by rotating the rotor to rotate the crankshaft and thereby rotates the rocking scroll provided on the crankshaft. The compressed refrigerant gas is discharged into the hermetic container to pass through the gap between the hermetic container and the stator and the gap between the rotor and the stator and is supplied through a discharge pipe to a refrigerator. Meanwhile, lubricating oil stored in the hermetic container is raised in a passageway in the crankshaft by the pressure-feeding action of an oil stirrer (twisted plate) provided in the passageway during the rotation of the crankshaft and supplied as a sealing oil and a lubricating oil to sliding portions of the compression unit and the like.
A hermetic rotary compressor having such a configuration causes deformation in the crankshaft because the torque increases when the refrigerant is compressed and the torque decreases when the high pressure refrigerant is discharged. The deformation in the crankshaft results from the load that the crankshaft receives from the rocking scroll and is increased during the rotation at higher speeds and under higher loads. As a result, vibrations and noises are generated.
To mitigate such vibrations and noises, conventional hermetic rotary compressors typically include components called balance weights attached on the axial ends of the rotor. Here, the balance weights are desirably made of a material that has a high specific gravity and allows no magnetic flux from the rotor to pass therethrough (low magnetic permeability), and brass is typically used. The brass is, however, expensive and it is desirable not to use the brass to reduce costs.
To dispense with the balance weights, a conventional rotor described in Patent Literature 1 has a through-opening, which is unbalanced with respect to the shaft hole as the center, in at least one axial end of the rotor. This configuration in the conventional technique described in Patent Literature 1 allows the rotor to produce the effect of the balance weights.